The present invention relates to an apparatus and a process for producing molten metal (which term includes metal alloys), in particular although by no means exclusively iron, from metalliferous feed material, such as ores, partially reduced ores and metal-containing waste streams, in a metallurgical vessel containing a molten bath.
The present invention relates particularly to a molten metal bath-based direct smelting apparatus and a process for producing molten metal from a metalliferous feed material.
A process that produces molten metal directly from ores (and partially reduced ores) is generally referred to as a xe2x80x9cdirect smelting processxe2x80x9d.
One known direct smelting process, which is generally referred to as the Romelt process, is based on the use of a large volume, highly agitated slag bath as the medium for smelting top-charged metal oxides to metal and for post-combusting gaseous reaction products and transferring the heat as required to continue smelting metal oxides. The Romelt process includes injection of oxygen enriched air or oxygen into the slag via a lower row of tuyeres to provide slag agitation and injection of oxygen into the slag via an upper row of tuyeres to promote post-combustion. In the Romelt process the metal layer that forms below the slag is not an important reaction medium.
Another known group of direct smelting processes that are slag-based is generally described as xe2x80x9cdeep slagxe2x80x9d processes. These processes, such as DIOS and AISI processes, are based on forming a deep layer of slag. As with the Romelt process, the metal layer below the slag layer is not an important reaction medium.
Another known direct smelting process which relies on a molten metal layer as a reaction medium, and is generally referred to as the HIsmelt process, is described in International application PCT/AU96/00197 (WO 96/31627) in the name of the applicant.
The HIsmelt process as described in the International application comprises:
(a) forming a molten bath having a metal layer and a slag layer on the metal layer in a vessel;
(b) injecting into the bath:
(i) a metalliferous feed material, typically metal oxides; and
(ii) a solid carbonaceous material, typically coal, which acts as a reductant of the metal oxides and a source of energy; and
(c) smelting the metalliferous feed material to metal in the metal layer.
The HIsmelt process also comprises post-combusting reaction gases, such as CO and H2, released from the bath in the space above the bath with oxygen-containing gas and transferring the heat generated by the post-combustion to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials.
The HIsmelt process also comprises forming a transition zone above the nominal quiescent surface of the bath in which there are ascending and thereafter descending droplets or splashes or streams of molten metal and slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
A preferred form of the HIsmelt process is characterized by forming the transition zone by injecting carrier gas, metalliferous feed material, solid carbonaceous material and optionally fluxes into the bath through lances that extend downwardly and inwardly through side walls of the vessel so that the carrier gas and the solid material penetrate the metal layer and cause molten material to be projected from the bath.
This form of the HIsmelt process is an improvement over earlier forms of the process which form the transition zone by bottom injection of carrier gas and solid carbonaceous material through tuyeres into the bath which causes droplets, splashes and streams of molten material to be projected from the bath.
The applicant has carried out extensive pilot plant work on the above-described preferred form of the HIsmelt process in a pilot plant vessel having a hearth diameter of 2.74 m. The size of pilot plant vessel, whilst rated to produce 100,000 tonnes of molten metal per year, is smaller than that of a commercial size vessel. A commercial size vessel is one that is capable of producing at least 500,000 tonnes of molten metal per year. Typically, a commercial size vessel is one that is capable of producing 1-1.5 million tonnes of molten metal per year. Necessarily, such a commercial size vessel would have a hearth diameter that is larger than 2.74 m. During and subsequent to the pilot plant work the applicant has carried out development work on a vessel for a commercial operation. The present invention was made in the course of that development work.
According to the present invention there is provided a vessel which produces metal from a metalliferous feed material by a direct smelting process, which vessel contains a molten bath having a metal layer and a slag layer on the metal layer and has a gas continuous space above the slag layer, which vessel includes:
(a) a shell;
(b) a hearth formed of refractory material having a base and sides in contact with the molten bath.
(c) side walls which extend upwardly from the sides of the hearth and are in contact with the slag layer and the gas continuous space
(d) one or more than one lance/tuyere extending downwardly into the vessel and injecting an oxygen-containing gas into the vessel above the metal and slag layer;
(e) a plurality of pairs of lances/tuyeres extending downwardly and inwardly into the vessel and injecting feed material which includes metalliferous feed material and carbonaceous material with a carrier gas into the molten bath so as to penetrate the metal layer and generate a bath-derived gas flow which carries molten material upwardly from the metal layer and the slag layer as splashes, droplets and streams of molten material and forms a transition zone in the gas continuous space, the pairs of lances/tuyeres being spaced around the circumference of the vessel, one lance/tuyere of each pair injecting feed material, primarily metalliferous feed material, at a temperature of at least 200xc2x0 C. (hereinafter referred to as the xe2x80x9chotxe2x80x9d lance/tuyere), and the other lance/tuyere of each pair injecting feed material, primarily carbonaceous material, at a temperature less than 200xc2x0 C. (hereinafter referred to as a xe2x80x9ccoldxe2x80x9d lance/tuyere); and
(f) a means for tapping molten metal and slag from the vessel.
Preferably the vessel is a commercial size vessel that is capable of producing at least 500,000 tonnes of molten metal per year.
Preferably the hot lance/tuyere injects feed material at a temperature of at least 600xc2x0 C.
The term xe2x80x9cprimarilyxe2x80x9d in the context of a nominated feed material is understood to mean that at least 50% by weight of the feed material injected through a given lance/tuyere is the nominated feed material.
Preferably the feed material is in a solid state. The feed material may be in liquid or gas state as well as solid state. By way of example, the carbonaceous material may be in solid, liquid or gas state.
Preferably the hot lance/tuyere injects no volatile carbonaceous material.
The hot lance/tuyere may inject non-volatile carbonaceous material, such as char.
Typically, the host lance/tuyere injects metalliferous feed material and non-volatile carbonaceous material at the temperature of at least 200xc2x0 C.
The injection of feed material through the cold lance/tuyere is not confined to carbonaceous material and, by way of example, may include plant reverts.
Preferably the lances/tuyeres of any given pair of lances/tuyeres are positioned with respect to each other so that the lances/tuyeres inject feed material towards a point spaced from the pair of lances/tuyeres.
The term xe2x80x9csmeltingxe2x80x9d is understood herein to mean thermal processing wherein chemical reactions that reduce metal oxides takes place to produce liquid metal.
The term xe2x80x9cmetal layerxe2x80x9d is understood herein to mean that region of the bath that is predominantly metal. Specifically, the term covers a region or zone that includes a dispersion of molten slag in a metal continuous volume.
The term xe2x80x9cslag layerxe2x80x9d is understood herein to mean that region of the bath that is predominantly slag. Specifically, the term covers a region or zone that includes a dispersion of molten metal in a slag continuous volume.
The metalliferous feed material may be any suitable material and in any suitable form. A preferred metalliferous feed material is an iron-containing material. The iron-containing material may be in the form of ores, partially reduced ores, DRI (direct reduced iron), iron carbide, millscale, blast furnace dust, sinter fines, BOF dust or a mixture of such materials.
In the case of partially reduced ores, the degree of pre-reduction may range from relatively low levels (eg to FeO) to relatively high levels (eg 70 to 95% metallisation).
The carrier gas for the hot lances/tuyeres may be the same as or different to the carrier gas for the cold lances/tuyeres.
It is preferred that the carrier gas for the cold lances/tuyeres contain no oxygen or be an oxygen-deficient gas.
It is preferred that the carrier gas comprise nitrogen.
The transition zone is quite different to the slag layer. By way of explanation, under stable operating conditions of the process the slag layer comprises gas bubbles in a liquid continuous volume whereas the transition zone comprises splashes, droplets, and streams of molten material, predominantly slag, in a gas continuous volume.
Preferably oxygen-containing gas injected into the vessel post-combusts reaction gases, such as carbon monoxide and hydrogen, generated in the molten bath, in a top space (including the transition zone) above the surface of the molten bath and the heat generated by the post-combustion is transferred to the metal layer to maintain the temperature of the molten bathxe2x80x94as is essential in view of endothermic reactions in that layer.
The injection of the solid feed material, such as in the form of metalliferous feed material and solid carbonaceous material, through the pairs of lances/tuyeres towards and thereafter into the metal layer has the following consequences:
(a) the momentum of the injected solid material/carrier gas (and any liquid or gaseous feed material) causes the solid material/carrier gas to penetrate the metal layer;
(b) the carbonaceous material, typically coal, is devolatilised and thereby produces gas in the metal layer;
(c) carbon predominantly dissolves into the metal and partially remains as solid;
(d) the metalliferous material is smelted to metal by carbon derived from injected carbon as described above in item (c) and the smelting reaction generates carbon monoxide gas; and
(e) the gases transported into the metal layer and generated via devolatilisation and smelting produce significant buoyancy uplift of molten metal, solid carbon and slag (which is drawn into the metal layer as a consequence of solid/gas injection) from the metal layer which results in upward movement of splashes, droplets and streams of molten material, and these splashes, droplets, and streams entrain further slag as they move upwardly.
Preferably the location and operating parameters of the one or more than one lance/tuyere that inject the oxygen-containing gas and the operating parameters that control the transition zone are selected so that:
(a) the oxygen-containing gas is injected towards and penetrates the transition zone;
(b) the transition zone extends upwardly around the lower section of the or each lance/tuyere and thereby shields to some degree the side walls of the vessel from the combustion zone generated at the end of the or each lance/tuyere; and
(e) there is gas continuous space described as a xe2x80x9cfree spacexe2x80x9d which contains practically no metal and slag around the end of the or each lance/tuyere.
Item (c) above is an important feature because it makes it possible for reaction gases in the top space of the vessel to be drawn into the region at the end of the or each lance/tuyere and be post-combusted in the region.
Preferably the vessel includes at least two oxygen-containing gas injection lances/tuyeres.
Preferably the vessels contain a relatively high (but not too high) slag inventory and the amount of slag is used as a means of controlling the process.
The term xe2x80x9crelatively high slag inventoryxe2x80x9d may be understood in the context of the amount of slag compared to the amount of meal in the vessel.
According to the present invention there is also provided a direct smelting process for producing metal from a metalliferous feed material in a metallurgical vessel as described above, which process includes the steps of:
(a) forming a molten bath having a metal layer and a slag layer on the metal layer in the vessel;
(b) injecting feed material which includes metalliferous feed material and carbonaceous material with a carrier gas into the molten bath via a plurality of pairs of lances/tuyeres, with one lance/tuyere of each pair injecting feed material, primarily metalliferous feed material, at a temperature of at least 200xc2x0 C., and the other lance/tuyere of each pair injecting feed material, primarily carbonaceous material, at a temperature of less than 200xc2x0 C., and smelting metalliferous material in the metal layer, whereby the feed material and carrier gas injection causes gas flow from the metal layer, which gas flow entrains molten material in the metal layer and carries molten material upwardly as splashes, droplets and streams and forms a transition zone in a gas continuous space in the vessel above the slag layer;
(c) smelting metalliferous feed material to metal in the metal layer; and
(d) injecting an oxygen-containing gas into the vessel via one or more than one lance/tuyere and post-combusting reaction gases released from the molten bath, whereby ascending and thereafter descending splashes, droplets and streams of molten material facilitate heat transfer to the molten bath, and whereby the transition zone minimises radiation heat loss from the vessel via the side walls in contact with the transition zone.